public virtual class SampleSuperClass implements SampleInterface {
    public void doSomething(){
        system.debug('Learning Apex Programming Language');
    }
    public virtual String sayWhatToDo(){
        return 'Do Visualforce workbook ...';
    }
    
    public list<String> allThingsToDo(String  firstthing){
        List<String> strs=new List<String>();
        strs.add(firstthing);
        strs.add('Do Apex Workbook ...');
        strs.add('Do Visualforce Workbook ...');
        strs.add('Watch some TV for relaxation ...');       
        return strs;
    }
    
    // You can also have additiomal methods if you want
    public void printThingsToDo(list<String> strs){
        for(string s:strs)
            System.debug(s);
    }    
}